ScienceShot: Measles Transmission—As Seen From Space

Light punctuates the darkness in this satellite image of Niger and northern Nigeria. In a new paper in Science, scientists show that such pictures can help them explain and predict outbreaks of measles in the area. Researchers suspected that the seasonal surges in measles—a major childhood killer—were caused by people moving into Niger's cities at the start of the dry season, but they didn't have an easy way to quantify those movements. Researchers at Princeton University and Pennsylvania State University, State College, wondered whether they could use changes in nighttime light, both from electrical lights and fires, as a proxy for population density. It was an "off-the-wall idea," says Matthew Ferrari, one of the scientists, but it worked. In the paper, the team shows that upswings in brightness correlate well with measles outbreaks. Nighttime shots could find much wider use as an indicator of population density, the researchers say, for instance, in studies of economic development or during refugee crises.

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